Towards network slice availability

ABSTRACT

A method and system for providing a NS instance satisfying a requested availability of a NSI comprises obtaining at least one VNFD for a VNF composing the NS, the VNFD being associated with at least one absolute availability value guaranteed according to at least one DF; obtaining an availability value of NFVI on which the VNF is to be deployed; determining a minimum availability value for a NS instance of the NS; selecting a VNF DF and RM for the VNF DF such that the product of the absolute availability value of the VNF DF, taking into account the selected RM, and of the availability value of the NFVI is greater than or equal to the minimum availability value for the NS instance; and instantiating the NS instance by instantiating at least one VNF instance according to the at least one selected VNF DF and corresponding RM.

PRIORITY STATEMENT UNDER 35 U.S.C. S.119(E) & 37 C.F.R. S.1.78

This non-provisional patent application claims priority based upon theprior U.S. provisional patent application entitled “Towards networkslice availability”, application No. 62/715,913, filed Aug. 8, 2018, inthe name of Toeroe.

TECHNICAL FIELD

The present disclosure relates to Network Function Virtualisation (NFV)and Network Slicing.

BACKGROUND

Network Slicing is a new paradigm of telecommunications networksvirtualization. A Network Slice is an end-to-end virtualized network,which provides communication services according to a set of potentiallystringent quality of service parameters such as latency andavailability. It may be deployed on top of network services as definedby the ETSI-NFV specifications. Namely a network slice instance can bedeployed as a composition of nested and concatenated network serviceinstances.

SUMMARY

There is provided a method for providing a network service (NS) instancesatisfying a requested availability of a network slice instance (NSI),comprising: obtaining at least one virtual network function (VNF)descriptor (VNFD) comprising at least one absolute availability valueguaranteed according to at least one deployment flavor (DF) for the NSinstance; obtaining an availability value of a network functionvirtualization infrastructure (NFVI); obtaining criteria for selectingat least one VNF and obtaining a redundancy model, based on the at leastone absolute availability value of the at least one VNF descriptor andthe availability value of the NFVI; selecting the at least one VNF forproviding the NS instance based on the criteria; and instantiating a NSincluding at least one VNF instance corresponding to the at least oneselected VNF, according to the redundancy model, thereby providing theNS instance.

The NS instance may be a composition of a plurality of VNF instances.

An availability value of the NS instance may be calculated as a productof an availability value of the redundancy model and the availabilityvalue of the NFVI.

The availability value of the NS instance may be greater than therequested availability of the NSI.

The NSI may be a composition of a plurality of NS instances.

An availability value of the NSI may be calculated as a product of theavailability values of the plurality of NS instances in the NSI.

The VNFD may comprise an absolute availability value for the DF,A_(VNF-DF).

The VNFD may comprise a plurality of DFs and, for each DF, an absoluteavailability value, A_(VNF-DF).

The VNFD may further comprise information concerning which DFs of theVNF are designed to be used for VNF level redundancy.

The VNFD may further comprise information concerning a redundancycapability for each DF of the VNF that is designed to be used for VNFredundancy.

The VNFD may further comprise information concerning communication needsof redundant VNF instances.

There is no need for VNF redundancy for a VNF DF if

$A_{{VNF} - {DF}} > \frac{A_{NSI}}{A_{NFVI}}$

is satisfied, where A_(VNF-DF) is the availability of the VNF DF,A_(NFVI) is the availability of the NFVI on which the VNF instance is tobe deployed, and A_(NSI) is the availability of the NSI.

There is a need for VNF redundancy for a VNF DF if

$A_{{VNF} - {DF}} \leq \frac{A_{NSI}}{A_{NFVI}}$

is satisfied, where A_(VNF-DF) is the availability of the VNF DF,A_(NFVI) is the availability of the NFVI on which the VNF instance is tobe deployed, and A_(NSI) is the availability of the NSI.

The M and N values for the redundancy model may be chosen to satisfy

${{R{M\left( A_{{VNF} - {DF}} \right)}} > \frac{A_{NSI}}{A_{NFVI}}},$

where N is the number of VNF instances, M is the number of redundant VNFinstances, and where RM(A_(VNF-DF)) is the function calculating anavailability value of the redundancy model used with the VNF DF based onthe availability A_(VNF-DF) of the VNF DF, A_(NFVI) is the availabilityof the NFVI on which the VNF instance is to be deployed, and A_(NSI) isthe availability of the NSI.

There is provided a system for providing a network service (NS) instancesatisfying a requested availability of a network slice instance (NSI)comprising processing circuits and a memory, the memory containinginstructions executable by the processing circuits whereby the system isoperative to execute any of the steps of the previous method.

There is provided a non-transitory computer readable media having storedthereon instructions for providing a network service (NS) instancesatisfying a requested availability of a network slice instance (NSI),the instructions comprising any of the steps of the previous method.

The method(s) and system(s) provided herein present improvements to theway prior NFV systems operate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a 1:1 redundancy model.

FIG. 2 is a schematic illustration of a 3:1 redundancy model.

FIG. 1 is a schematic illustration of single-homed link redundancy.

FIG. 2 is a schematic illustration of dual-homed link redundancy.

FIGS. 5a and 5b are flowcharts of methods for providing a networkservice (NS) instance satisfying a requested availability of a networkslice instance (NSI).

FIG. 6 is a schematic illustration of the ETSI NFV referencearchitectural framework with its main components.

FIG. 7 is a schematic illustration of another virtualizationenvironment.

DETAILED DESCRIPTION

Various features and functions will now be described with reference tothe figures to fully convey the scope of the disclosure to those skilledin the art.

Many aspects will be described in terms of sequences of actions orfunctions. It should be recognized that some functions or actions couldbe performed by specialized circuits, by program instructions beingexecuted by one or more processors, or by a combination of both.

Further, some functions can be partially or completely embodied in theform of computer readable carrier or carrier wave containing anappropriate set of computer instructions that would cause a processor tocarry out the techniques described herein.

Some functions/actions may occur out of the order noted in the sequenceof actions or simultaneously. Furthermore, in some illustrations, someblocks, functions or actions may be optional and may or may not beexecuted; these are generally illustrated with dashed lines.

Within ETSI-NFV there is a discussion concerning how to ensure theavailability of a network slice based on the availabilitycharacteristics of the composing network services and their composingelements. Current techniques are based on categorization, which is notsufficient.

The method and system provided herein are based on the perspective thata network slice instance (NSI) is a composition of network service (NS)instances. These NS instances recursively can be decomposed into aconcatenation of Virtual Network Functions (VNFs), which may be deployedredundantly.

Composition/concatenation of non-redundant instances means that thetotal availability is calculated as the product of the availability ofindividual instances. Since the availability values are less than one,using a scale of zero to one, the multiplication implies that eachindividual availability needs to be greater than the requested total.

Assuming that the VNFs used to build the NS provide the absoluteavailability their deployment flavors guarantee and that a networkprovider knows the availability of its NFV infrastructure (NFVI), it ispossible to provide the criteria for selecting the VNFs and theirredundancy model.

This requires modifications to the current standards (specifically theVNF descriptor) to provide the absolute availability values and someadditional characteristics.

Advantageously, with the method and system provided herein, the VNFs donot need to provide all their internal details to the network operators,yet the network operators can build network services appropriate forrequested availability of network services and in turn network slices.

Designing Network Slice for Certain Availability Overall Considerations

Since a network slice instance (NSI) is deployed in the NFV environmentas a concatenation of one or more network service (NS) instances [seeNetwork Functions Virtualisation (NFV)—Network Operator Perspectives onNFV priorities for 5G, Feb. 21, 2017,http://portal.etsi.org/NFV/NFV_White_Paper_5G.pdf] we can say that NSIavailability depends on the availability of these NS instances, any ofwhich may be a nested instance. Note that if two NS instances areredundant and backing up each other we can consider them as nested NSinstance.

Accordingly, the NSI is available when all of the NS instances areavailable, which can be formulated as the product of the availability ofthe NS instances (A_(NSi)).

A _(NSI) =A _(NS1) *A _(NS2) * . . . * A _(NSn)   (1)

Since typically an NS instance availability is less than 100% orA_(NSi)<1, the multiplication in equation (1) implies that at minimumthe availability of each NS instance needs to be greater than the targetavailability of the NSI, ∀A_(NSi)>A_(NSI).

Each of the NS instances themselves are compositions of VNF instancesand nested NS instances. Unfolding the nested NS instances, the NSinstance becomes a concatenation of VNFs, some or all of which might bedeployed with redundant instances.

If the redundant instances of each given VNF as an NS are considered, itcan be said that the availability of such an NS instance depends on theavailability of the redundant VNF instances (each with the availabilityof A_(VNF)) and the availability of the NFVI (A_(NFVI)) on which theyare deployed. Thus, NS instance availability (A_(NS)) is:

A_(NS) =A _(NFVI) *RM(A _(VNF))   (2)

The NFVI availability can be considered as a whole, or as its differentsubsets or components hosting the different VNF instances.

The Redundancy Model (RM) function, equation (2), depends on theredundancy model used with the VNF instances, but in generalRM(A_(VNF))≥A_(VNF). That is, using some redundancy improves theavailability of the individual VNF instances, i.e. RM(A_(VNF))>A_(VNF),while using no redundancy RM(A_(VNF))=A_(VNF).

Considering (1) and (2), to achieve a given availability for a networkslice instance (A_(NSI)), it is clear that since ∀A_(NSi)>A_(NSI) theconditions of A_(NFVIi)>A_(NSi)>A_(NSI) and RM(A_(VNFi))>A_(NSi)>A_(NSI)need to be fulfilled. This means that the availability of all NSscomposing the network slice instance has to be greater than the targetedavailability for the network slice instance. Further, A_(NFVIi)indicates the availability of the NFVI on which the ith NS is built andA_(VNFi) is the availability of the VNF composing it.

In table 1 three different configurations were proposed to achievedifferent resiliency levels represented by NS resiliency classes. Eachrow proposed a selection of NFVI components and redundancy models of theVNFs and Virtual Links (VLs) to achieve a given NS resiliency class.However, the above considerations suggest that this approach may not besatisfactory, and it is necessary to know the absolute availabilityvalue a VNF can provide.

TABLE 1 Examples of network service resiliency configuration Networkservice Storage Compute Network service VFNs Link resiliency resourceresource redundancy redun- class reliability reliability Level TypeTechnique dancy High High High VNF 1 + 1 Local + Redun- and Geo dantVNFC redun- dual- dancy homed Medium Medium Medium VNF 1 + 1 Local +Redun- and Geo dant VNFC redun- single- dancy homed Low Regular RegularVNFC N + K Local Link redun- aggre- dancy gation

With respect to table 1, let consider only two different resiliencyclasses and define resiliency class “high” with an availability of equalto or greater than 99.999% and “low” if the availability is below99.999%. This means that if this classification is applied individuallyto the different NFVI resources represented in the columns and if theavailability each of them is equal to 99.999% (or A=0.99999), then theyare each considered of the category “high” as the first row of the tableshows. If these different resources are used to compose an NS, then theavailability of the resources needs to be multiplied to calculate theavailability of the composed NS. Since all the composing resources havean availability A=0.99999 any multiplication will result in anavailability lower than A=0.99999 (e.g. 0.99999*0.99999=0.9999800001),which, according to the definition, falls into the “low” category. Themore such resources are required for the NS the more the overallavailability falls below the availability expected by the “high”category.

Considering the redundancy models with respect to (2), they can improvethe availability of the individual VNF instances.

Consideration of VNF-Internal Redundancy

The VNF is a black box with respect to its internal redundancy for theNFV-Management and Orchestration (MANO) (NFV-MANO). The NFV-MANO doesnot manage nor is aware of the redundancy applied to the VNF Component(VNFC) instances. Instead the NFV-MANO instantiate a VNF according tothe Deployment Flavor (DF) selected and follows the instantiation levelsand scaling policies associated with the DF.

The scaling policies and instantiation levels dictate the number of VNFCinstances the NFV-MANO should instantiate for each VNFC. Sinceredundancy is reflected in the number of VNFC instances, it is safe toassume that scale levels of a DF of a VNF reflects the redundancy modelused within the VNF for each VNFC. Note that different VNFCs may utilizedifferent redundancy models within the same VNF and may be scaleddifferently. It is possible that a given VNFC is used with differentredundancy models in different DFs of the same VNF and accordingly itmay be scaled differently in different DFs. That is, the scaling policyassociated with a DF takes into consideration both the performance andthe redundancy requirements for each of the VNFCs used in the DF.

Therefore, it is better to know the absolute availability a VNF DFprovides than the redundancy model(s) used by that DF for the VNFCs. Inthis respect however, it is expected that the different instantiationlevels of a DF and its associated scaling policies are provided in theVNF Descriptor (VNFD) in such a way that the availability indicated forthe DF is guaranteed at each instantiation level considering a 100%reliable NFVI i.e. A_(NFVI)=1. Thus, A_(VNF-DF) is given according to(2) for the case when an instance of the VNF is deployed with the givenDF under the ideal condition.

A _(NS)=1*A _(VNF-DF)

When this DF is deployed on a less than ideal NFVI, then withoutVNF-level redundancy the NS availability achievable can be calculatedas:

A _(NS) =A _(NFVI) *A _(VNF-DF)

Or the VNF DF can be selected according to the target NS availabilityand the available NFVI availability as:

$\begin{matrix}{A_{{VNF} - {DF}} \geq \frac{A_{NS}}{A_{NFVI}}} & (3)\end{matrix}$

Depending on the NFVI resources and VNFs at disposal, this availabilitymay not be sufficient for the NS, in which case the VNF instances needto be deployed redundantly. Redundant deployment of VNF instances isalways the case in geo-redundant configurations, i.e. when disasterrecovery is a requirement.

Availability estimation for the 1+1 and 1:1 redundancy models

In the 1+1 and 1:1 redundancy models, each VNF instance has a redundantVNF instance as protection. The protecting VNF instance may also beactive, in which case the two VNFs share the actual workload. Theprotecting VNF instance may alternatively be a standby for thefirst/active VNF instance.

The 1+1 redundancy model is the active-active redundancy model whereboth instances provide services as well as backing up each other. 1:1indicates the active-standby redundancy (see FIG. 1) where one instanceprovides the service, the other does not, it only serves as abackup/standby for the first, in case it fails.

The document ETSI GS NFV-REL 003 V1.1.2 (2016-07) Network FunctionsVirtualisation (NFV); Reliability; Report on Models and Features forEnd-to-End Reliabilityhttps://docbox.etsi.org/ISG/NFV/Open/Publications_pdf/Specs-Reports/NFV-REL%20003v1.1.2%20-%2OGS%20-%20E2E%20reliability%20models%20report.pdfprovides further information concerning the redundancy models discussedherein.

In either case, the NFV-MANO does not manage the active/standby roleassignments of the VNF instances nor is it aware of these roles.

The NFV-MANO is only responsible to provide virtualized resources ofenough capacity that allow full protection for the entire workloadhandled by the VNF instance-pair so that there is no service degradationin case one of the instances fails. Hence, the availability estimationis the same for both redundancy models and reflects the availabilitywith respect to the resources provided by the NFV system.

FIG. 1 depicts an example of an instance of a simple Network Service(NS), which is composed of one VNF. In the NS instance, the VNF has anactive (VNF^(a)) and a standby (VNF^(b)) instance. They are hosted onthe same NFVI, but they form an anti-affinity group and therefore relyon different physical resources within the NFVI.

To calculate the overall availability in this case, it is assumed thatthe NS instance is available when the NFVI and at least one of the VNFinstances are available. Therefore, the NS instance is not available ifthe NFVI or both VNF instances fail, and:

A _(NS) =A _(NFVI)*(1−(F _(VNF) _(a) *F _(VNF) _(b) ))

-   -   where, F_(VNF)=1−A_(VNF)

A _(NS) =A _(NFVI)*(1−((1−A _(VNF) _(a) )*(1−A _(VNF) _(b) )))

If VNF^(a) and VNF^(b) are deployed using the same DF, which providesthe same availability for all instantiation levels, then:

A_(VNF) _(a) =A_(VNF) _(b)

Therefore, the NS instance availability becomes:

A _(NS) =A _(NFVI)*(1−(1−A _(VNF) _(a) )²)

A _(NS) =A _(NFVI)*(1−(1+A _(VNF) _(a) ²−2*A _(VNF) _(a) ))

Which can be re-written as:

A _(NS) =A _(NFVI)*(2*A _(VNF) −A _(VNF) ²)   (4)

Equation (4) provides the RM function for the 1+1 and 1:1 redundancymodels.

Availability Estimation for the N+M and N:M Redundancy Models

As in the previous case the NFV-MANO does not manage nor is aware of theactive/standby roles of the VNF instances. It only manages the number ofVNF instances based on the volume of the workload handled by theinstances. Therefore, from the NFV-MANO perspective, these modelsindicate the number of VNF instances required to serve the workloadwithout protection (N) and the number of VNF instance that can fail (M)before any workload degradation occurs; i.e. M instances provideprotection for the workload capacity of N instances. Hence, from NFVperspective only resource level availability can be considered, i.e. anyof the M redundant instances can replace any of the N instances.

It is assumed that we have an instance of a simple NS with one VNF,which has four instances as shown in FIG. 2. The VNF instances use the3:1 redundancy model which means that, out of the four, three are activeVNF instances (e.g. VNF^(a), VNF^(b) and VNF^(c)) and one is standby(VNF^(d)). All of these are deployed on the same NFVI, but form ananti-affinity group, which means they rely on different physicalresources.

Since there is only one redundant VNF instance (M=1), if more than one(generally, more than M) VNF instance(s) fail(s), the overallavailability goal is not met, i.e. the service becomes degraded or failscompletely. To avoid this, the minimum number of VNF instances N must beavailable, which is three in this case. As a result, the availability ofthe NS instance would be:

A _(NS) =A _(NFVI)*(the probability of having at least three availableVNF instances)

A _(NS) =A _(NFVI)*(A _(VNF) _(a) *A _(VNF) _(b) *A _(VNF) _(c) *F_(VNF) _(d) +A _(VNF) _(a) *A _(VNF) _(b) *F _(VNF) _(c) *A _(VNF) _(d)+A _(VNF) _(a) *F _(VNF) _(b) *A _(VNF) _(a) *A _(VNF) _(d) +F _(VNF)_(a) *A _(VNF) _(b) *A _(VNF) _(c) *A _(VNF) _(d) +A _(VNF) _(a) *A_(VNF) _(b) *A _(VNF) _(c) *A _(VNF) _(d) )

Assuming that all the VNF instances are deployed with the same VNF DF,then:

A_(VNF) _(a) =A_(VNF) _(b) =A_(VNF) _(c) =A_(VNF) _(d) =A_(VNF)

Therefore, the availability of the NS instance is:

A _(NS) =A _(NFVI)*(4*A _(VNF) ³ *F _(VNF) +A _(VNF))

Accordingly, to keep the NS instance available, the NFVI has to beavailable and, in addition, a selection of three VNF instances out ofthe four, or a selection of four VNF instances out of the four must beavailable. This means that the above can be re-written as:

$A_{NS} = {A_{NFVI}*\left( {{\begin{pmatrix}4 \\3\end{pmatrix}*A_{VNF}^{3}*\left( {1 - A_{VNF}} \right)^{1}} + \ {\begin{pmatrix}4 \\4\end{pmatrix}*A_{VNF}^{4}*\left( {1 - A_{VNF}} \right)^{0}}} \right)}$

This equation can be generalized as:

$\begin{matrix}{{A_{NS} = {A_{NFVI}*\left( {\sum_{k = 0}^{M}\ {\begin{pmatrix}{N + M} \\{N + k}\end{pmatrix}A_{VNF}^{N + k}*\left( {1 - A_{VNF}} \right)^{M - k}}} \right)}}{{{{{{where}\mspace{14mu} N} > 0}\&}M} \geq 0}} & (5)\end{matrix}$

Equation (5) provides the RM function for the N+M and N:M redundancymodels.

Availability estimation for single- and dual-homed link redundancy

The availability of an NS instance also depends on the availability ofthe virtual links (VLs) interconnecting the different VNF instances. Forthe estimation of the availability of the virtual links single- anddual-homing are considered.

To begin with, two simple cases of VL redundancy, in an NS with twoVNFs, are considered:

-   -   NS₁ uses single-homing as redundancy for the VLs between the        instances of VNF1 and VNF2, as shown in FIG. 3.    -   In contrast, NS₂ uses dual-homing as shown in FIG. 4.

The assumption is that the redundant VLs form anti-affinity groups andtherefore rely on different physical resources.

To calculate the availability for these NS instances, it is assumedthat:

A_(VNF1) _(a) =A_(VNF1) _(b) and A_(VNF2) _(a) =A_(VNF2) _(b)

A_(VL) _(a) =A_(VL) _(b) =A_(VL) _(c) =A_(VL) _(d) =A_(VL)

Then, NS₁ is available if the NFVI is available and:

-   -   I. VNF1^(a) and VNF2^(a) and at least one of VL^(a) and VL^(b)        is available; or    -   II. VNF1^(b) and VNF2^(b) and at least one of the VL^(c) and        VL^(d) is available; or    -   III. Both above conditions are met.

Therefore:

A _(I) =A _(II) =A _(VNF1)*(1−F _(VL) ²)*A _(VNF2)

A _(NS) ₁ =A _(NFVI)*(1−F ₁ ^(I) *F _(II))

A _(NS) ₁ =A _(NFVI)*(131 (1−A _(VNF1)*(1−F _(VL) ²)*A _(VNF2))²)   (6)

NS₂ is available if at least one of VNF1^(a) and VNF1^(b) is availableand one of the VNF2^(a) and VNF2^(b) is available and at least one linkbetween a couple of available VNFs is available. A_(I) and F_(I)indicate the availability and the failure (i.e. non-availability) forcase I, and A_(II) and F_(II) indicate the same for case II.

As a result:

A _(NS) ₂ =A _(NFVI)*(4*A _(VNF1) *F _(VNF1) *A _(VNF2) *F _(VNF2) *A_(VL)+2*A _(VNF1) *F _(VNF1) *A _(VNF) ²*(1−F _(VL) ²)+2*A _(VNF1) *A_(VNF2) *F _(VNF2)*(1−F _(VL) ²)+A _(VNF1) ² *A _(VNF2) ²*(1−F _(VL) ⁴))  (7)

Note that the same logic applies within the VNF with respect to theredundancy and availability of the links interconnecting VNFC instances.

ANALYSIS OF SERVICE RESILIENCY CONFIGURATION EXAMPLES

After determining the RM(A_(VNF)) function for different redundancyconfigurations the resiliency configurations of table 1 can be furtheranalyzed. The question is whether different redundancy models of VNFinstances and VLs could be used depending the availability provided bydifferent VNFs or VNF DFs (A_(VNF)) and the NFVI (A_(NFVI)).

In fact, equations (2) and (3) propose that if a given value is desiredfor A_(NS), a provider can select a NFVI with lower availability andprovide the same NS availability by constructing an RM(A_(VNF)) withhigher availability. Alternatively, one can exploit a more reliable NFVIor redundancy to compensate for a lower A_(VNF). This is demonstrated inthe following examples based on (4), (5), (6), and (7), by deployingdifferent VNFs (or different DFs of a VNF) to achieve a certainavailability.

It is assumed that the minimum absolute availabilities a VNF can provideare reflected in the DFs of the VNF, each of which is defined accordingto some VNF-internal redundancy model known by the VNF vendor. That is,the different instantiation levels of a DF and its associated scalingpolicies are defined in such a way in the VNFD that all of themguarantee the availability indicated for the DF on a 100% reliable NFVIi.e. A_(NFVI)=1.

Example 1 VNF Availability Compensating for Weaker Redundancy Model

Assuming there is a need for an NS with four 9s availability(A_(NS)=0.9999). The availability of the NFVI is A_(NFVI)=0.99999.

The NS can be built in different ways, i.e. using VNFs from differentvendors or using different DFs of the same VNF. Let assume DF1 of a VNFprovides two 9s availability for a VNF instance, i.e. A_(VNF1)=0.99, andDF2 of the VNF provides three 9s availability for a VNF instance, i.e.A_(VNF2)=0.999. Since A_(VNF1)<A_(VNF2) the NS₁ is composed with tworedundant VNF instances using DF1 in the 1+1 redundancy model; while NS₂is composed with three VNF instances of DF2 with the 2+1 redundancymodel used for NS₂.

Using equation (4) for NS₁, the estimated availability is:

A _(NS) ₁ =A _(NFVI)*(2*A _(VNF1) −A _(VNF1) ²)=0.999890001

Using equation (5) for NS₂ its estimated availability is:

$A_{NS_{2}} = {{A_{NFVI}*\left( {\sum_{k = 0}^{M}\ {\begin{pmatrix}{N + M} \\{N + k}\end{pmatrix}A_{{VNF}\; 2}^{N + k}*\left( {1 - A_{VNF2}} \right)^{M - k}}} \right)} = 0.99998700202998}$

Thus, despite the weaker redundancy model used in NS₂, it meets theexpected four 9s availability due to the significantly higheravailability that the DF2 provides. On the other hand, NS₁, even withthe stronger redundancy model, cannot be used to meet the expectations.

This example demonstrates that depending on the availability of the VNFinstances, it is possible to achieve better availability (e.g. four 9sversus three 9s) with a redundancy model typically considered to be weak(i.e. for lower availability in the third row of the table 1). Thus, theredundancy model by itself does not characterize the achievableavailability. A VNF with a higher availability can compensate for thelower capability of the redundancy model. Moreover, using a strongerredundancy model with such a VNF results in lower utilization ofresources.

The same logic applies within the VNF with respect to the redundancy andavailability of the VNFC instances. This reinforce the point madeearlier that characterizing the VNF by the redundancy model used for theVNFC instances is not sufficient to characterize the overallavailability a VNF or its DF can provide.

Example 2 NFVI Availability Compensating for VNF Availability

Considering the NSs of the previous example and deploying them on anNFVI with six 9s availability (A_(NFVI)=0.999999), if all otherconditions remain the same, the calculations result in:

A _(NS) ₁ =0.9998990001>0.999890001

A _(NS) ₂ =0.999996002002998>0.99998700202998

Thus, the availability of the NSs increased in both cases, whichindicates that the NFVI availability can compensate to some extent forthe shortcomings of the VNF. In case of NS2 deployed with the N+Mredundancy model, such improvement of the NFVI availability results inachieving even five 9s availability. However, for NS₁ deployed with the1+1 redundancy model it is still not enough to provide the targeted four9s.

These results, together with the previous ones, show how the combinationof the NFVI, the VNF availabilities and the redundancy model need to beconsidered.

Example 3 VNF Availability Compensating for VL Redundancy

To compare the NS availability when used with different VNFs anddifferent VL redundancy models the cases shown in FIGS. 3 and 4 areconsidered.

Here, the NS is built from two interconnected VNFs: VNF1 and VNF2.Again, VNF instances with different DFs providing differentavailabilities are used and are interconnected through links withdifferent redundancies. That is, NS₁ uses single-homing as redundancyfor the VLs between the instances of VNF1 and VNF2, while NS₂ usesdual-homing. The following is further assumed:

-   -   For all cases A_(VL)=0.9999 and A_(NFVI)=0.99999    -   For NS₁ A_(VNF1)=A_(VNF2)=0.999    -   For NS₂, A_(VNF1)=A_(VNF2)=0.99

Then, using equations (6) and (7) respectively the availability of theNS instance is estimated as:

A_(NS) ₁ =0.999986003999060229421196205896

A_(NS) ₂ =0.99978997240817622513735959601

This shows that NS₁ deployed with single-homing (the weaker linkredundancy) but built with instances of higher availability can providethe targeted four 9s availability. On the other hand, NS₂, deployed withdual-homing, does not provide the expected four 9s due to the loweravailability of the VNF instances used, i.e. the availability of theVNFs used in NS₁ compensates for the difference in the VL redundancy.This again shows that using a better link redundancy model by itselfdoes not necessarily provide better availability. It needs to beconsidered together with the other composing elements of the NS andtheir redundancy.

Analysis and Conclusions

These examples demonstrate that, at the time of the NS design, it isnecessary to know the absolute availability that can be provided by thedifferent elements that can be used for composing an NS. With thisinformation an appropriate combination can be selected and combinedusing appropriate redundancy models as necessary for the VNF and VLinstances.

In case of the VNF, the information necessary includes the minimumabsolute availability each DF indicated in the VNFD can provide. Each DFneeds to be designed in such a way that this absolute availability ismaintained throughout the different instantiation levels described forthe DF when scaling according to the applicable scaling policies alsodescribed in the VNFD.

Since redundant deployment of a VNF is reflected in the NS Descriptor(NSD), the VNFD needs to include enough information based on which aprovider can design an NS for a desired availability. The informationnecessary for this includes:

-   -   Indicating the DF(s) of the VNF, which are designed to be used        for VNF level redundancy.    -   The redundancy capability of such DF(s) in terms of the N and M        ratio of VNF instances that can be used together, if any.    -   The communication needs of the redundant VNF instances, if any.

Note that since the NFV-MANO does not manage and is not aware of theactive/standby roles of the VNF instances, the N and M ratio onlyprovides information in terms of redundant capacity of resourcesprovided by the NFV system.

Considering (1) according to which ∀A_(NSi)>A_(NSI) needs to befulfilled, that is, the availability of any NS instance used for an NSIneeds to provide an availability greater than the availability of theNSI. This means that the availability required by the NSI provides alower bound of availability for the NS design.

Considering the availability of the NFVI, and the different VNF DFs, itcan be determined whether VNF redundancy is necessary for eachapplicable VNF DF. If the following condition (8) is satisfied, no VNFredundancy is required from an availability perspective for the givenVNF DF. A_(NFVI) is the availability of the NFVI on which the VNFinstance is to be deployed. A_(NSI) is the availability of the NSI forwhich the VNF instance is considered.

$\begin{matrix}{A_{{VNF} - {DF}} > \frac{A_{NSI}}{A_{NFVI}}} & (8)\end{matrix}$

If this is not the case, it may still be possible to use the VNF in aredundant configuration. For this, the considered VNF DF needs tosupport redundant configurations. If so, the N and M values can be usedto determine if condition (9) can be satisfied.

$\begin{matrix}{{R{M\left( A_{{VNF} - {DF}} \right)}} > \frac{A_{NSI}}{A_{NFVI}}} & (9)\end{matrix}$

Note that the multiplication in (1) means that satisfying (9) for eachNS_(i) composing the NSI does not mean that the overall NSI availabilityrequirement is met, as it has been shown at the resiliencyconfiguration. (8) and (9) are only the necessary conditions thatprovide the starting point for the design.

Requirements

It shall be possible to indicate in the VNFD the minimum absoluteavailability value provided by a deployment flavor of the VNF.

The minimum absolute availability value of a VNF deployment flavor shallbe indicated as if the VNF was deployed on an NFVI with 100%availability.

Each instantiation level of a given VNF deployment flavor and theassociated scaling policies shall guarantee the minimum absoluteavailability value specified for the deployment flavor.

It shall be possible to indicate whether a deployment flavor of the VNFis designed for redundant deployment of VNF instances and the applicableredundancy capability in terms of redundant capacity.

It shall be possible to indicate if redundant deployment of the VNFrequires interconnection between the VNF instances and itscharacteristics.

Referring to FIG. 5a , there is provided a method 500 for providing anetwork service (NS) instance satisfying a requested availability of anetwork slice instance (NSI), comprising: obtaining, step 505, at leastone virtual network function (VNF) descriptor (VNFD) comprising at leastone absolute availability value guaranteed according to at least onedeployment flavor (DF) for the NS instance; obtaining, step 510, anavailability value of a network function virtualization infrastructure(NFVI); obtaining, step 515, criteria for selecting at least one VNF andobtaining a redundancy model, based on the at least one absoluteavailability value of the at least one VNF descriptor and theavailability value of the NFVI; selecting, step 520, the at least oneVNF for providing the NS instance based on the criteria; andinstantiating, step 525, a NS including at least one VNF instancecorresponding to the at least one selected VNF, according to theredundancy model, thereby providing the NS instance.

The NS instance may be a composition of a plurality of VNF instances.

An availability value of the NS instance may be calculated as a productof an availability value of the redundancy model and the availabilityvalue of the NFVI.

The availability value of the NS instance may be greater than therequested availability of the NSI.

The NSI may be a composition of a plurality of NS instances.

An availability value of the NSI may be calculated as a product of theavailability values of the plurality of NS instances in the NSI.

The VNFD may comprise an absolute availability value for the DF,A_(VNF-DF).

The VNFD may comprise a plurality of DFs and, for each DF, an absoluteavailability value, A_(VNF-DF).

The VNFD may further comprise information concerning which DFs of theVNF are designed to be used for VNF level redundancy.

The VNFD may further comprise information concerning a redundancycapability for each DF of the VNF that is designed to be used for VNFredundancy.

The VNFD may further comprise information concerning communication needsof redundant VNF instances.

There is no need for VNF redundancy for a VNF DF if

$A_{{VNF} - {DF}} > \frac{A_{NSI}}{A_{NFVI}}$

is satisfied, where A_(VNF-DF) is the availability of the VNF DF,A_(NFVI) is the availability of the NFVI on which the VNF instance is tobe deployed, and A_(NSI) is the availability of the NSI.

There is a need for VNF redundancy for a VNF DF if

$A_{{VNF} - {DF}} \leq \frac{A_{NSI}}{A_{NFVI}}$

is satisfied, where A_(VNF-DF) is the availability of the VNF DF,A_(NFVI) is the availability of the NFVI on which the VNF instance is tobe deployed, and A_(NSI) is the availability of the NSI.

The M and N values for the redundancy model may be chosen to satisfy

${{R{M\left( A_{{VNF} - {DF}} \right)}} > \frac{A_{NSI}}{A_{NFVI}}},$

where N is the number of VNF instances, M is the number of redundant VNFinstances, and where RM(A_(VNF-DF)) is the function calculating anavailability value of the redundancy model used with the VNF DF based onthe availability A_(VNF-DF) of the VNF DF, A_(NFVI) is the availabilityof the NFVI on which the VNF instance is to be deployed, and A_(NSI) isthe availability of the NSI.

Referring to FIG. 5b , there is provided a method 550 for providing anetwork service (NS) satisfying a requested availability of a networkslice. The method comprises obtaining, step 555, at least one virtualnetwork function (VNF) descriptor (VNFD) for a VNF composing the NS, theVNFD being associated with at least one absolute availability valueguaranteed according to at least one deployment flavor (DF); obtaining,step 560, an availability value of a network function virtualizationinfrastructure (NFVI) on which the VNF is to be deployed; determining,step 565, a minimum availability value for a NS instance of the NS;selecting, step 570, a VNF DF and redundancy model (RM) for the VNF DFsuch that the product of the absolute availability value of the VNF DF,taking into account the selected RM, and of the availability value ofthe NFVI is greater than or equal to the minimum availability value forthe NS instance; and instantiating, step 575, the NS instance byinstantiating at least one VNF instance according to the at least oneselected VNF DF and corresponding RM.

In this context, absolute availability corresponds to the VNFavailability considering an NFVI availability of 100%. I.e. theavailability the VNF by itself can achieve when given all the resourcesneeded. Typically, the availability of the VNF and of the NFVI are lowerthan 100% and the measured availability of a VNF includes and thereforeis relative to the availability of the NFVI. In practice, since eachNFVI may have a different availability it becomes very difficult to comeup with a single VNF availability value. Therefore, using a theoreticalNFVI availability of 100% eliminates this problem. In practice, there isno such NFVI availability of 100%, and VNF availability under such anassumption needs to be a calculated, for which there is currently nostandard calculation methodology.

The network slice instance (NSI) may be a concatenation of one or moreNS instances. The NS instance may be a composition of a plurality of VNFinstances. The availability value of the NS instance may be greater thana requested availability of the NSI. An availability value of the NSImay be calculated as a product of the availability values of theplurality of NS instances in the NSI. The VNFD may comprise a pluralityof DFs and information concerning an absolute availability value,A_(VNF-DF) may be associated to each DF. The VNFD may comprise aplurality of DFs and information concerning which DFs of the VNF aredesigned to be used for VNF level redundancy may be associated to eachDF. Information concerning a redundancy capability for each DF of theVNF that is designed to be used for VNF redundancy may be associated toeach DF. Information concerning communication needs of redundant VNFinstances may be associated to each DF. The information may be obtainedfrom a VNF product characteristic descriptor. Alternatively, theinformation may be stored within the VNFD.

There is no need for VNF redundancy for a VNF DF

$A_{{VNF} - {DF}} > \frac{A_{NSI}}{A_{NFVI}}$

is satisfied, where A_(VNF-DF) is the availability of the VNF DF,A_(NFVI) is the availability of the NFVI on which the VNF instance is tobe deployed, and A_(NSI) is the availability of the NSI. There is a needfor VNF redundancy for a VNF DF if

$A_{{VNF} - {DF}} \leq \frac{A_{NSI}}{A_{NFVI}}$

is satisfied, where A_(VNF-DF) is the availability of the VNF DF,A_(NFVI) is the availability of the NFVI on which the VNF instance is tobe deployed, and A_(NSI) is the availability of the NSI. The M and Nvalues for the redundancy model may be chosen to satisfy

${{R{M\left( A_{{VNF} - {DF}} \right)}} > \frac{A_{NSI}}{A_{NFVI}}},$

where N is the number of VNF instances, M is the number of redundant VNFinstances, and where RM(A_(VNF-DF)) is the function calculating anavailability value of the redundancy model used with the VNF DF based onthe availability A_(VNF-DF) of the VNF DF, A_(NFVI) is the availabilityof the NFVI on which the VNF instance is to be deployed, and A_(NSI) isthe availability of the NSI.

FIG. 6 presents the ETSI NFV reference architectural framework with itsmain components, in which steps described herein may be executed.

Similar to FIG. 6, FIG. 7 is a schematic block diagram illustrating avirtualization environment 700 in which functions described herein maybe implemented.

In some embodiments, some or all of the functions described herein maybe implemented as virtual components executed by one or more virtualmachines or containers implemented in one or more virtual environments700 hosted by one or more of hardware nodes 730.

The functions may be implemented by one or more applications 720 (whichmay alternatively be called software instances, virtual appliances,network functions, virtual nodes, virtual network functions, etc.)operative to implement steps of some methods according to someembodiments. Applications 720 run in virtualization environment 700which provides hardware 730 comprising processing circuitry 760 andmemory 790. Memory 790 contains instructions 795 executable byprocessing circuitry 760 whereby application 720 is operative to provideany of the relevant features, benefits, and/or functions disclosedherein.

Virtualization environment 700, comprises general-purpose orspecial-purpose network hardware devices 730 comprising a set of one ormore processors or processing circuitry 760, which may be commercialoff-the-shelf (COTS) processors, dedicated Application SpecificIntegrated Circuits (ASICs), or any other type of processing circuitryincluding digital or analog hardware components or special purposeprocessors. Each hardware device may comprise memory 790-1 which may benon-persistent memory for temporarily storing instructions 795 orsoftware executed by the processing circuitry 760. Each hardware devicesmay comprise one or more network interface controllers 770 (NICs), alsoknown as network interface cards, which include physical networkinterface 780. Each hardware devices may also include non-transitory,persistent, machine readable storage media 790-2 having stored thereinsoftware 795 and/or instruction executable by processing circuitry 760.Software 795 may include any type of software including software forinstantiating one or more virtualization layers 750 (also referred to ashypervisors), software to execute virtual machines 740 or containers aswell as software allowing to execute functions described in relationwith some embodiments described herein.

Virtual machines 740 or containers, comprise virtual processing, virtualmemory, virtual networking or interface and virtual storage, and may berun by a corresponding virtualization layer 750 or hypervisor. Differentembodiments of the instance of virtual appliance 720 may be implementedon one or more of virtual machines 740 or containers, and theimplementations may be made in different ways.

During operation, processing circuitry 760 executes software 795 toinstantiate the hypervisor or virtualization layer 750, which maysometimes be referred to as a virtual machine monitor (VMM).Virtualization layer 750 may present a virtual operating platform thatappears like networking hardware to virtual machine 740 or to acontainer.

As shown in FIG. 7, hardware 730 may be a standalone network node, withgeneric or specific components. Hardware 730 may comprise antenna 7225and may implement some functions via virtualization. Alternatively,hardware 730 may be part of a larger cluster of hardware (e.g. such asin a data center or customer premise equipment (CPE)) where manyhardware nodes work together and are managed via management andorchestration (MANO) 7100, which, among others, oversees lifecyclemanagement of applications 720.

Virtualization of the hardware is in some contexts referred to asnetwork function virtualization (NFV). NFV may be used to consolidatemany network equipment types onto industry standard high volume serverhardware, physical switches, and physical storage, which can be locatedin data centers, and customer premise equipment.

In the context of NFV, a virtual machine 740 or container is a softwareimplementation of a physical machine that runs programs as if they wereexecuting on a physical, non-virtualized machine. Each of virtualmachines 740 or container, and that part of the hardware 730 thatexecutes that virtual machine, be it hardware dedicated to that virtualmachine and/or hardware shared by that virtual machine with others ofthe virtual machines 740 or containers, forms a separate virtual networkelements (VNE).

Still in the context of NFV, Virtual Network Function (VNF) isresponsible for handling specific network functions that run in one ormore virtual machines 740 or containers on top of hardware networkinginfrastructure 730 and corresponds to application 720 in FIG. 7.

In some embodiments, one or more radio units 7200 that each include oneor more transmitters 7220 and one or more receivers 7210 may be coupledto one or more antennas 7225. Radio units 7200 may communicate directlywith hardware nodes 730 via one or more appropriate network interfacesand may be used in combination with the virtual components to provide avirtual node with radio capabilities, such as a radio access node or abase station.

In some embodiments, some signaling can be effected with the use ofcontrol system 7230 which may alternatively be used for communicationbetween the hardware nodes 730 and the radio units 7200.

There is provided a system 600, 700 for providing a network service (NS)instance satisfying a requested availability of a network slice instance(NSI) comprising processing circuits and a memory. The memory containsinstructions executable by the processing circuits whereby the system isoperative to obtain at least one virtual network function (VNF)descriptor (VNFD) for a VNF composing the NS, the VNFD being associatedwith at least one absolute availability value guaranteed according to atleast one deployment flavor (DF); obtain an availability value of anetwork function virtualization infrastructure (NFVI) on which the VNFis to be deployed; determine a minimum availability value for a NSinstance of the NS; select a VNF DF and redundancy model (RM) for theVNF DF such that the product of the absolute availability value of theVNF DF, taking into account the selected RM, and of the availabilityvalue of the NFVI is greater than or equal to the minimum availabilityvalue for the NS instance; and instantiate the NS instance byinstantiating at least one VNF instance according to the at least oneselected VNF DF and corresponding RM.

The network slice instance (NSI) may be a concatenation of one or moreNS instances. The NS instance may be a composition of a plurality of VNFinstances. The availability value of the NS instance may be greater thana requested availability of the NSI. An availability value of the NSImay be calculated as a product of the availability values of theplurality of NS instances in the NSI. The VNFD may comprise a pluralityof DFs and information concerning an absolute availability value,A_(VNF-DF) may be associated to each DF. The VNFD may comprise aplurality of DFs and information concerning which DFs of the VNF aredesigned to be used for VNF level redundancy may be associated to eachDF. Information concerning a redundancy capability for each DF of theVNF that is designed to be used for VNF redundancy may be associated toeach DF. Information concerning communication needs of redundant VNFinstances may be associated to each DF. The information may be obtainedfrom a VNF product characteristic descriptor. Alternatively, theinformation may be stored within the VNFD.

There is no need for VNF redundancy for a VNF DF if

$A_{{VNF} - {DF}} > \frac{A_{NSI}}{A_{NFVI}}$

is satisfied, where A_(VNF-DF) is the availability of the VNF DF,A_(NFVI) is the availability of the NFVI on which the VNF instance is tobe deployed, and A_(NSI) is the availability of the NSI. There is a needfor VNF redundancy for a VNF DF if

$A_{{VNF} - {DF}} \leq \frac{A_{NSI}}{A_{NFVI}}$

is satisfied, where A_(VNF-DF) is the availability of the VNF DF,A_(NFVI) is the availability of the NFVI on which the VNF instance is tobe deployed, and A_(NSI) is the availability of the NSI. The M and Nvalues for the redundancy model may be chosen to satisfy

${{R{M\left( A_{{VNF} - {DF}} \right)}} > \frac{A_{NSI}}{A_{NFVI}}},$

where N is the number of VNF instances, M is the number of redundant VNFinstances, and where RM(A_(VNF-DF)) is the function calculating anavailability value of the redundancy model used with the VNF DF based onthe availability A_(VNF-DF) of the VNF DF, A_(NFVI) is the availabilityof the NFVI on which the VNF instance is to be deployed, and A_(NSI) isthe availability of the NSI.

There is provided a non-transitory computer readable media 790-2 havingstored thereon instructions for providing a network service (NS)instance satisfying a requested availability of a network slice instance(NSI), the instructions comprising any of the steps described herein.

Modifications and other embodiments will come to mind to one skilled inthe art having the benefit of the teachings presented in the foregoingdescription and the associated drawings. Therefore, it is to beunderstood that modifications and other embodiments, such as specificforms other than those of the embodiments described above, are intendedto be included within the scope of this disclosure. The describedembodiments are merely illustrative and should not be consideredrestrictive in any way.

1. A method for providing a network service (NS) satisfying a requestedavailability of a network slice, comprising: obtaining at least onevirtual network function (VNF) descriptor (VNFD) for a VNF composing theNS, the VNFD being associated with at least one absolute availabilityvalue guaranteed according to at least one deployment flavor (DF);obtaining an availability value of a network function virtualizationinfrastructure (NFVI) on which the VNF is to be deployed; determining aminimum availability value for a NS instance of the NS; selecting a VNFDF and redundancy model (RM) for the VNF DF such that the product of theabsolute availability value of the VNF DF, taking into account theselected RM, and of the availability value of the NFVI is greater thanor equal to the minimum availability value for the NS instance; andinstantiating the NS instance by instantiating at least one VNF instanceaccording to the at least one selected VNF DF and corresponding RM. 2.The method of claim 1, wherein a network slice instance (NSI) is aconcatenation of one or more NS instances.
 3. The method of claim 1,wherein the NS instance is a composition of a plurality of VNFinstances.
 4. The method of claim 2, wherein the availability value ofthe NS instance is greater than a requested availability of the NSI. 5.The method of claim 2, wherein an availability value of the NSI iscalculated as a product of the availability values of the plurality ofNS instances in the NSI.
 6. The method of claim 1, wherein the VNFDcomprises a plurality of DFs and wherein information concerning anabsolute availability value, A_(VNF-DF) is associated to each DF.
 7. Themethod of claim 1, wherein the VNFD comprises a plurality of DFs andwherein information concerning which DFs of the VNF are designed to beused for VNF level redundancy is associated to each DF.
 8. The method ofclaim 6, wherein information concerning a redundancy capability for eachDF of the VNF that is designed to be used for VNF redundancy isassociated to each DF.
 9. The method of claim 6, wherein informationconcerning communication needs of redundant VNF instances is associatedto each DF.
 10. The method of claim 6, wherein the information isobtained from a VNF product characteristic descriptor and wherein theinformation is stored within the VNFD.
 11. (canceled)
 12. The method ofclaim 1, wherein there is no need for VNF redundancy for a VNF${{DF}\mspace{14mu}{if}\mspace{14mu} A_{{VNF} - {DF}}} > \frac{A_{NSI}}{A_{NFVI}}$is satisfied, where A_(VNF-DF) is the availability of the VNF DF,A_(NFVI) is the availability of the NFVI on which the VNF instance is tobe deployed, and A_(NSI) is the availability of the NSI.
 13. The methodof claim 1, wherein there is a need for VNF redundancy for a VNF DF if$A_{{VNF} - {DF}} \leq \frac{A_{NSI}}{A_{NFVI}}$ is satisfied, whereA_(VNF-DF) is the availability of the VNF DF, A_(NFVI) is theavailability of the NFVI on which the VNF instance is to be deployed,and A_(NSI) is the availability of the NSI.
 14. The method of claim 13,wherein M and N values for the redundancy model are chosen to satisfy${{R{M\left( A_{{VNF} - {DF}} \right)}} > \frac{A_{NSI}}{A_{NFVI}}},$where N is the number of VNF instances, M is the number of redundant VNFinstances, and where RM(A_(VNF-DF)) is the function calculating anavailability value of the redundancy model used with the VNF DF based onthe availability A_(VNF-DF) of the VNF DF, A_(NFVI) is the availabilityof the NFVI on which the VNF instance is to be deployed, and A_(NSI) isthe availability of the NSI.
 15. A system for providing a networkservice (NS) instance satisfying a requested availability of a networkslice instance (NSI) comprising processing circuits and a memory, thememory containing instructions executable by the processing circuitswhereby the system is operative to: obtain at least one virtual networkfunction (VNF) descriptor (VNFD) for a VNF composing the NS, the VNFDbeing associated with at least one absolute availability valueguaranteed according to at least one deployment flavor (DF); obtain anavailability value of a network function virtualization infrastructure(NFVI) on which the VNF is to be deployed; determine a minimumavailability value for a NS instance of the NS; select a VNF DF andredundancy model (RM) for the VNF DF such that the product of theabsolute availability value of the VNF DF, taking into account theselected RM, and of the availability value of the NFVI is greater thanor equal to the minimum availability value for the NS instance; andinstantiate the NS instance by instantiating at least one VNF instanceaccording to the at least one selected VNF DF and corresponding RM. Thesystem of claim 15, wherein a network slice instance (NSI) is aconcatenation of one or more NS instances.
 16. The system of claim 15,wherein the NS instance is a composition of a plurality of VNFinstances.
 17. The system of claim 16, wherein the availability value ofthe NS instance is greater than a requested availability of the NSI. 18.The system of claim 16, wherein an availability value of the NSI iscalculated as a product of the availability values of the plurality ofNS instances in the NSI.
 19. The system of claim 15, wherein the VNFDcomprises a plurality of DFs and wherein information concerning anabsolute availability value, A_(VNF-DF) is associated to each DF. 20.The system of claim 15, wherein the VNFD comprises a plurality of DFsand wherein information concerning which DFs of the VNF are designed tobe used for VNF level redundancy is associated to each DF.
 21. Thesystem of claim 20, wherein information concerning a redundancycapability for each DF of the VNF that is designed to be used for VNFredundancy is associated to each DF.
 22. The system of claim 20, whereininformation concerning communication needs of redundant VNF instances isassociated to each DF.
 23. The system of claim 19, wherein theinformation is obtained from a VNF product characteristic descriptor andwherein the information is stored within the VNFD.
 24. (canceled) 25.The system of claim 15, wherein there is no need for VNF redundancy fora VNF DF if $A_{{VNF} - {DF}} > \frac{A_{NSI}}{A_{NFVI}}$ is satisfied,where A_(VNF-DF) is the availability of the VNF DF, A_(NFVI) is theavailability of the NFVI on which the VNF instance is to be deployed,and A_(NSI) is the availability of the NSI.
 26. The system of claim 15,wherein there is a need for VNF redundancy for a VNF DF if$A_{{VNF} - {DF}} \leq \frac{A_{NSI}}{A_{NFVI}}$ is satisfied, whereA_(VNF-DF) is the availability of the VNF DF, A_(NFVI) is theavailability of the NFVI on which the VNF instance is to be deployed,and A_(NSI) is the availability of the NSI.
 27. The system of claim 26,wherein M and N values for the redundancy model are chosen to satisfy${{R{M\left( A_{{VNF} - {DF}} \right)}} > \frac{A_{NSI}}{A_{NFVI}}},$ ,where N is the number of VNF instances, M is the number of redundant VNFinstances, and where RM(A_(VNF-DF)) is the function calculating anavailability value of the redundancy model used with the VNF DF based onthe availability A_(VNF-DF) of the VNF DF, A_(NFVI) is the availabilityof the NFVI on which the VNF instance is to be deployed, and A_(NSI) isthe availability of the NSI.
 28. A non-transitory computer readablemedia having stored thereon instructions for providing a network service(NS) instance satisfying a requested availability of a network sliceinstance (NSI), the instructions comprising: obtaining at least onevirtual network function (VNF) descriptor (VNFD) for a VNF composing theNS, the VNFD being associated with at least one absolute availabilityvalue guaranteed according to at least one deployment flavor (DF);obtaining an availability value of a network function virtualizationinfrastructure (NFVI) on which the VNF is to be deployed; determining aminimum availability value for a NS instance of the NS; selecting a VNFDF and redundancy model (RM) for the VNF DF such that the product of theabsolute availability value of the VNF DF, taking into account theselected RM, and of the availability value of the NFVI is greater thanor equal to the minimum availability value for the NS instance; andinstantiating the NS instance by instantiating at least one VNF instanceaccording to the at least one selected VNF DF and corresponding RM.